My invention comprises improvements in a throttle valve system for use in controlling shift points and line pressure in an automatic transmission valve circuit. Examples of automatic transmission valve controls using throttle valve pressure as an indicator of engine torque are disclosed in U.S. Pat. No. 3,525,275 and 4,351,206, each of which is assigned to the assignee of this invention. In the valve system of the '275 patent a throttle valve in the form of a pressure regulating valve spool is connected mechanically by means of a lever arrangement or an actuator cable to the engine carburetor throttle. The output of that regulating valve is distributed to a throttle pressure booster, and the output of the booster in turn is used to establish shift points.
The shift points are determined by shift valves that are subjected to the output of the throttle pressure booster valve and to the output of a pressure governor Solenoid operated valves establish pressure forces on a downshift control valve that overrules the automatic upshifting and downshifting tendencies of the valve circuit of the '275 patent.
In the case of the control system of the '206 patent, line pressure is regulated for distribution to pressure servos for the transmission clutches and brakes. The line pressure regulator comprises a solenoid operated valve that establishes variable forces on a regulator valve element which in effect is a regulator similar to the throttle pressure regulator valve of the '275 patent although it performs a different regulating function.
I am aware of various electronic control systems for automatic transmissions that use a pilot operated throttle valve wherein the throttle valve is actuated by a varible force solenoid rather than a system such as those shown in the aforementioned patents. The output pressure of the solenoid valve acts directly on the regulating valve, either the pressure regulator or the throttle valve regulator. Examples of such systems are disclosed in U.S. Pat. Nos. 3,727,487 and 3,783,713. The latter patent uses a throttle valve or kickdown valve spool that is actuated by a solenoid but the solenoid force acts directly on a slide valve that is biased by a spring. This requires a solenoid force that is relatively high and the travel of the armature of the solenoid actuator for the valve is relatively large because of the necessity for long travel of the slide valve.
The system shown in the '487 patent avoids the necessity for using a spool valve that requires long travel and which is susceptible to valve sticking, but in that arrangement the pilot valve is subjected directly to the full output pressure of the pump. The system then is relatively unstable because pump pressure variations will cause corresponding variations in the throttle valve system as a whole.